Crosstalk may be simply defined as that situation when two signal carrying circuits extend close together where the existence of signaling currents in one circuit will tend to set up corresponding currents in the other. With the present trend for increasing transmission rates of electrical connecting devices, there followed the increasing demand for improved performance, particularly in the reduction of crosstalk at frequencies up to 100 MHz. As a consequence of this demand, the Telecommunications Industry Association (TIA) in cooperation with the Electronic Industries Association (EIA) recently developed a proposed standard for Category 5 components, where the transmission requirements of such components are characterized up to 100 MHz and are typically intended for emerging applications with transmission rates up to 100 Mbps. The standard is preliminarily identified as TSB40, Aug. 1992. The invention hereof relates to the hardware, but it is important to note that the hardware is only one major element of a communication system, while another major component is the transmission cable. Thus, it is important to insure the use of the correct connecting component or hardware that is compatible with the transmission characteristics of the cable. Such cables are typically high performance unshielded twisted-pair (UTP) cables, the performance characteristics of which are covered by EIA/TIA bulletin TSB-36.
Returning now to the component aspect of a transmission system, one of the more important test parameters for high performance electrical connector hardware, i.e. Category 5, is Near-End Cross-Talk (NEXT) Loss. This may be further defined as a measure of signal coupling from one circuit to another within a connector and is derived from swept frequency voltage measurements on short lengths of 100-ohm twisted-pair test leads terminated to the connector under test. A balanced input signal is applied to a disturbing pair of the connector while the induced signal on the disturbed pair is measured at the near-end of the test leads. In other words, NEXT loss is the way describing the effects of signal coupling causing portions of the signal on one pair to appear on another pair as unwanted noise. In any case, the worst case NEXT loss, see values below in TABLE I, for any combination of disturbing and disturbed pairs is determined by the formula:
NEXT (F).gtoreq.NEXT (16)-20 Log (F/16) where NEXT (16) is the minimum NEXT loss at 16 MHZ, F is frequency (in MHZ) in the range from 1 MHZ to the highest referenced frequency, and NEXT (F) is the performance at that frequency.
TABLE I ______________________________________ UTP Connecting Hardware NEXT Loss Limits As Specified in EIA/TIA Document TSB-40 Frequency Category 5 (MHz) (dB) ______________________________________ 1.0 &gt;65 4.0 &gt;65 8.0 62 10.0 60 16.0 56 20.0 54 25 52 31.25 50 62.5 44 100 40 ______________________________________
While problems associated with crosstalk have been known for years, as evidenced by U.S. Pat. Nos. 1,995,454 and 2,080,217 a major concern has only recently come to the forefront by the current demands for improved performance and higher signal transmission qualities. A recent development is represented by U.S. Pat. No. 5,186,647 to Denkmann et al. A major objective of the patent is to reduce crosstalk between specific conductors in a connector. A preferred embodiment thereof is a panel mount modular jack which includes a pair of lead frames, each comprising four, flat elongated conductors. The lead frames are mounted on top of each other and their conductors are all generally parallel and close to each other throughout a portion of the length of the conductors. The claimed improvement in crosstalk performance is achieved by a selected crossover pattern of the conductors without electrical contact being made because of a reentrant bend in the conductors in the crossover region.
The present invention, like the companion copending application, achieves Category 5 performance by a significant reduction in crosstalk with capacitive coupling through non-ohmic contact. Such performance, and the manner by which it is achieved in the present invention, will become apparent in the description which follows, particularly when read in conjunction with the accompanying drawings.